On May 29, CME logged the biggest trading day of its 165-year-history, with nearly 27 million contracts changing hands. That day a Fed official signaled the central bank's plan to ease its buying of U.S. bonds, which has kept interest rates low. The new tack kicked up market volatility and gave traders a need to hedge interest rates with futures contracts.

CME "stock is very interest rate-sensitive," former CME board member Robert Corvino says. "Volume has exploded."

It may be the case that many investors aren't looking to load up on bonds, given the potential for further losses as the Federal Reserve normalizes policy in the coming months and years – but someone still has to trade them, even on the way down.